That is irrelevant to the actual problem.  Qimage cannot print on portions of the paper that the driver does not allow; it cannot override the driver with margins that are less than the "Fixed" margins shown in QU's Margins dialog.  If the driver is allowing any software to print on that portion of the paper, all the inks should be working in that region.  Otherwise you have a physical problem with the printer.

If you look at the page margins in QU, make sure all "additional" margins are set to zero, then print.  If your "Fixed" margin shows .1167 in the QU margins dialog and you are actually getting .051, you have a paper feed problem because the driver will not allow anything to print short of the "Fixed" margin no matter what data you send to it.

By setting your top margin to 0.25, you are just bandaiding the paper feed problem and as a result, you'll lose vertical printable area.  Your bottom margin will be larger than what it should be as well.  One way you could prove this one way or the other is to print a "Fit to Page" size print (with crop on).  Your print size should be the printable area for the P400 so the print should be 8.266 x 10.766.  Your top margin should be .1167 and the bottom margin should be .1181.  If you end up getting an 8.266 x 10.766 print but the top margin is smaller (.05) and the bottom margin is larger (.185), you'll know the paper is not feeding properly.

Mike